Core drilling is used for performing different types of rock technological investigations, wherein a drill core is being drilled, picked up from the drill hole and analysed for different properties, mineral contents etc. Core drilling is an important function for the investigation and evaluation of a rock body, and the result of the core drilling is often the basis for decisions of great economic importance such as if, for example, an ore body is to be exploited or not.
In a previously known procedure for core drilling, a tubular, abrasive, drill bit which is arranged at the end of a tubular drill string is rotated against the rock intended for sampling. When drilling has been performed a certain determined distance, the drill string contains a correspondingly long drill core, which, after interrupting the rotational movement, is pulled up out of the drill string for analysis etc.
In respect of a normal core drilling procedure, it is drilled in the order between two and five meters before a drill core is picked up from the drill string.
In a previously known core drilling equipment, a core retrieving pipe is used, which during active drilling is positioned adjacent to the drill bit for receiving the drill core produced through the drilling. The core retrieving tube has the character of being an inner pipe inside the drill string and comprises, at the end which is turned away from the drill bit, engagement means for the co-operation with a catch tool, which after a completed drilling period is introduced into the drill string all the way to the core retrieving pipe, in order to be connected thereto in a operative position, whereupon the catch tool with connected core retrieving tube and a drill core being firmly held inside, can be pulled out from the drill string.
Core drilling is often performed at very great distances from the drill rig, in particular at great depths such as for example depths of 3000 m. At such great distances, the time for lowering of the core retrieving pipe and the time for lowering of the catch tool take considerable amounts of time. Also in respect of essentially shorter drilling distances, some hundreds of meters, lowering of these tools is a considerable part of the total operation time of the drill rig.
In respect of today's core drilling procedures, it is to a great extant up to the individual operator to determine when the core retrieving pipe and the catch tool respectively have reached their respective operative positions. This is had through i.a. control and observation of the equipment in different ways in order to determine when the respective tool has reached its respective operative position. Since the environment at a drill rig for core drilling is noisy and subjected to outside uncontrollable circumstances, experience has shown that it is difficult for the operator to determine when the respective tool has reached its operative position and thereby when the next step for operating the rig is to be initiated.
For that reason it is very common that the operator as a safety measure continues a lowering function such as flushing with flushing fluid against their respective tool, a long period of time after that the tool in fact has reached its operative position. This procedure of course contributes to the operational safety but can be economically very disadvantageous, since the total operational economy of the rig is essentially impaired with reduced production as a consequence.
Another aspect is that initiating the next step in a core drilling process before a tool (the core retrieving pipe or the catch tool) has reached it operative position results in erroneous function, possibly stop of operation and in any case an extended process.